The temperature sensor for the frame goes in the engine and is different from the temperature handles so that the electro -seasons that go on the radiator start.
I would try by removing the radiator temperature manocontact and literally putting it to a boil ", I mean putting it on the fire inside a container with water having previously taken two cables from the contacts.
With a canter or lamp see when closing the contracts when rising the temperature of the water and when that happens, in a thermometer that you will have already introduced into the water you look at what temperature it is located. So you know exactly what temperature the electros enter.
If the radiator temperature manocontaco works well, the option is that the temperature sensor is bad, but there is no resistance values that it has to give for each temperature.
If the radiator handocontact (for the electros), the temperature sensor (for the frame) and you say that you have changed the thermostat (it is supposed to be fine) are well, it only occurs to me that the water pump strap is not well tensioned or that the water pump is failing and there is not enough water passage to the radiator (eye, it can also be failure of the thermostat that you changed). Motor block, but does not rise so fast on the radiator because there is no water step and how the radiator temperature is what the electros jumps, although the engine temperature is high the electros do not jump or jump late.
Well, I have rolled up a lot, I hope you understand it. Luck.